Power transmission device for rotating a grader circle

ABSTRACT

A grader circle has an annular internal gear which is meshed with a gear carried at the bottom of a crank shaft. A pair of double-acting hydraulic actuators have their piston rods connected to the crank pin of the crank shaft and the circle is driven by alternate extensions and retractions of the piston rods. The cylinders of the actuators are swivelly connected to the circle-carrying frame by means of pin structures which are fixed to and swivel with the cylinders as the piston rods are extended and retracted. The pin structures terminate in cams which engage shiftable valve stems of a reversing valve to automatically reverse the flow of fluid to the actuators when the piston rods of the actuators reach the ends of their strokes.

United States Patent 1 Hanser 1March 20, 1973 [54] POWER TRANSMISSION DEVICE FOR ROTATING A GRADER CIRCLE [75] Inventor: Paul Edmund I-llanser, Moline, Ill.

[73] Assignee: Deere & Company, Moline, Ill.

[22] Filed: Aug. 20, 1971 [21] Appl. No: 173,577

Related US. Application Data [62] Division of Ser. No. 20,726, March 18, 1970.

[52] US. Cl ..172/792, 172/796 [51] Int. Cl. ..E02f 3/12 [58] Field of Search 172/781, 791, 792, 793, 796

[56] References Cited UNITED STATES PATENTS 2,811,139 10/1957 Lado ..172/792 X 1,844,058 2/1932 Dean ..l72/796 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Stephen C. Pellegrino Attorney-41. Vincent I-larsha, Harold M. Knoth, William A. Murray and John M. Nolan [57] ABSTRACT A grader circle has an annular internal gear which is meshed with a gear carried at the bottom of a crank shaft. A pair of double-acting hydraulic actuators have their piston rods connected to the crank pin of the crank shaft and the circle is driven by alternate extensions and retractions of the piston rods. The cylinders of the actuators are swivelly connected to the circlecarrying frame by means of pin structures which are fixed to and swivel with the cylinders as the piston rods are extended and retracted. The pin structures terminate in cams which engage shiftable valve stems of a reversing valve to automatically reverse the flow of fluid to the actuators when the piston rods of the actuators reach the ends of their strokes.

9 Claims, 4 Drawing Figures PATENTEDHARZOIBYS 3.721303 SHEET 10F 3 ll, I72 58 7o I I l' v I FIG. 3

INVENTOR.

PAUL E. HANSER PATENTEUHARZOISB 3 7 1,303

SHEET 2 OF 3 INVENTOR. PAUL E. HANSER PATEMTEE MAR 2 0 I973 SHEET 3 BF 3 wol l N VEN TOR. PAUL E. HANSER POWER TRANSMISSION DEVICE FOR ROTATING A GRADER CIRCLE CROSS REFERENCE TO RELATED APPLICATION This is a division of application Ser. No. 20,726, filed Mar. 18,1970.

BACKGROUND OF THE INVENTION This invention relates to a power transmission device for rotating a grader circle and more particularly relates to a power transmission device that includes a crank shaft rotatably driven by alternate extension and retraction of the piston rods of a pair of double-acting hydraulic actuators and a reversing valve that is automatically actuated to reverse the flow of fluid to the actuators when the piston rods are at the ends of their strokes.

Such power transmission devices are generally known and one is illustrated in U. S. Pat. No. 2,81 1,139 issued to Lado on Oct. 29, 1951. These prior art devices have the disadvantages of lacking the compactness desired for general application and of being relatively difficult and/or expensive to manufacture.

SUMMARY OF THE INVENTION According to the present invention, there is provided a power transmission device for rotatably driving a grader circle and more particularly there is provided a device which includes a pair of double-acting hydraulic actuators and a reversing valve automatically actuated for reversing the flow of fluid to the actuators when the actuators are at the ends of their strokes.

An object of the invention is to provide a circle drive that is compact.

A more specific object is to provide a reversing valve that is reliable and easy to manufacture.

Still a more specific object is to swivelly mount the actuators on pin structures and to provide cams on the pin structures for actuating the reversing valve as the actuators swivel between positions corresponding to positions wherein the piston rods are at the ends of their strokes.

These and other objects will become apparent from the appended drawings and ensuing description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the front end portion of a motor grader in which a power transmission device constructed according to the above-mentioned principles is embodied for drivingthe circle of the grader.

FIG. 2 is an enlarged plan view of the power transmission device, the circle and the circle supporting structure shown in FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2 but showing the reversing valve removed.

FIG. 4 is a schematic view of the fluid system for controlling the power transmission device, showing the reversing valve in section with the valve bores in a common plane for convenience and showing the system in the condition for driving the grader circle counterclockwise.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is illustrated a motor grader 10 of which only the forward portion is shown. It is to be understood that the rearward portion of the grader 10 is conventional in that it includes the motor and drive wheels of the grader. The grader 10 includes an arched frame 12 supported at its front by a pair of wheels 14 and supported at its rear by the rearward portion of the grader (not shown). An operators station 16 is mounted on the rear portion of the frame 12 and located thereat are appropriate controls (not shown) for the grader 10. It is here noted that all directions, for example, right and left and counterclockwise and clockwise are made according to the view of a forwardly facing operator at the station 16.

A triangular drawbar 18 is generally symmetrical with respect to an axis AA along a line bisecting a forward corner 20. The forward corner 20 is connected by means of a ball and socket joint 22 to the forward underside of the frame 12 and a pair of hydraulic actuators 24 and 26 are respectively connected between right and left rear corners 28 and 30 of the drawbar l8 and right and left sides of a rotatable saddle structure 32 carried by the frame 12. The actuators 24 and 26 are extensible and retractable for adjusting the drawbar l8 angularly about the ball and socket joint 22. A third hydraulic actuator 34 is connected between the frame 12 and a ball 36 on the right side of the drawbar l8 and is extensible and retractable for shifting the drawbar sideways on the joint 22.

A circle 40 is rotatably supported, in a manner well known in the art, from the underside of the drawbar 18 and a power transmission device 42 is provided for rotatably driving the circle 40 relative to the drawbar 18 to adjust the working angle of a blade 44 that is fixed to the circle 40.

It is to be understood that the application of the power transmission device 42 as a means for rotating the grader circle 40 is only a representative use and that the device 42 may be used wherever a rotatable output is desired.

The power transmission device 42 includes right and left double-acting hydraulic actuators 46 and 48, respectively. The actuators 46 and 48 include respective cylinders 50 and 52 and piston rods 54 and 56.

Fixed to the upper and lower surfaces of the drawbar 18 are a pair of vertically spaced, transversely extending, horizontal plates 58 and 60, respectively. The actuators 46and 48 are mounted between the plates at transversely spaced positions on the opposite sides of the line AA by vertically extending mounting pin structures 62 and 64. The mounting pin structures 62 and 64 are fixedly secured to the forward ends of the cylinders 50 and 52, respectively, and are journaled at their tops and bottoms for swivelling movement in the plates 58 and 60. A crank shaft is located on the line AA forwardly of the mounting pin structures 62 and 64 and is also journaled for rotation in the plates 58 and 60. The piston rods 54 and 56 are vertically spaced from each other and the crank shaft 70 has a centrally located crank pin 72 to which is journaled bearing members74 and 76 fixed to the ends of the piston rods 54 and 56. A gear 78is fixed at the bottom of the crank shaft 70 and is meshed with an internal annular gear 80 carried by the circle 40. Thus, it can be seen that clockwise rotation of the crank shaft 70 will drive the circle clockwise andthat counterclockwise rotation of the crank shaft 70 will drive the circle counterclockwise.

When the actuators 46 and 48 are respectively in eithertheir fully extended or fully retracted positions,

the crank pin 72 will be at one of its pair of on-center positions relative to each actuator. The strokes of the piston rods 54 and 56 are 90 out of phase so that when the crank pin 72 reaches an on-center position relative to one actuator, the other actuator will drive the crank pin over center thereby ensuring that subsequent extension or retraction of the one actuator will be effective to drive the crank shaft 70 in the desired direction of rotation. It will beappreciated that except for the momentary periods that the crank pin 72 is at an on center position, the driving force of both of the actuators 46 and 48 is used to rotate the circle 40.

The direction of fluid flow to and from the actuators 46 and 48, hence, the extension and retraction of the piston rods 54 and 56, is controlled by a reversing valve 82. The reversing valve 82 includes an elongated generally rectangular valve body 84 which is mounted on the upper plate 58 between and centered with respect to the upper ends of the mounting pin structures 62 and 64 and is disposed half on one side and half on the other side of a line B-Bextending through the rotational centers of the pin structures 62 and 64. First and second pairs of upper and lower vertically disposed valve bores 86, 88 and 90, 92, respectively, extend lengthwise through the forward and rearward halves of the valve body 84. For convenience and clarity, the first pair of upper and lower valve bores 86 and 88 are respectively shown at the top and bottom of FIG. 4 in a plane common with the second pair of upper and lower valve bores 90 and 92.

The upper bores 86 and 90 and the lower bores 88 and 9'2 are respectively interconnected medially their ends by fluid passages 94 and 96. Also, medially of the ends of the bores 86 and 88 are respectively an inlet port'98 and a return port 100. A conduit 102 conveys fluid from a source of fluid pressure, shown as a pump 104, to the inlet port 98 and a conduit 106 connects the return port 100 to a reservoir'108. A direction control valve 1 is connected in the conduits 102 and 106 and is shiftable from a central neutral position wherein fluid 'flow is blocked to and from the reversing valve 82, to a first active position wherein the inlet and outlet ports 98 and 100 are respectively connected to the pump 104 and reservoir 106 and to a second active position wherein the inlet and outlet ports 98 and 100 are respectively connected to the reservoir 108 and the pump 104.

The bores 86, 88, 80 and 92 are respectively intersected by right control ports 112, 1 14, 118 and l 18 and by respective left control ports 120, 122, 124 and 126. The right control ports 112 and 116 are interconnected to each other and to a first work port 128 of the right actuator 46 by a fluid conduit means 130 and the right control ports 114 and 116 are interconnected to each otherand to a second work port 132 of the right actuator 46 by a conduit means 134. Similarly, the left control ports 120 and 126 are interconnected to each other and to a first work port 136 of the left actuator 48 by a fluid conduit means 138 and the left control ports 122 and 124 are interconnected to each other and to a second work port 140 of the left actuator 48 by a conduit means 142. I

The right and left control ports are respectively selectively connected or disconnected via the medial portions of the bores to either the inlet port 98 or the outlet port 100 by the operation of identical valve members 144 positioned in the opposite ends of each bore.

The'valve members 144 each include an elongated sleeve-like member 146 having an outer end portion 148 threadedly received in the end of a bore and held in the desired axial position by a lock nut 150. The members 146 each have a central bore 152 intersected by radial ports 154, the bore 152 and the ports 154 forming a fluid passage for fluid communication between either the inlet or return ports 98 and 100 respectively, and the right and left groups of control ports. The inner end 156 of each of the members 146 terminates in a planar, annular valve seat 158 and a hollow valve element 160 is normally seated against the seat 158, as shown in the bores 90 and 92 of FIG. 4, to block flow to and from the bore 152. The valve elements 160 are unseated to the positions shown in the bores 86 and 88 of FIG. 4 by valve stems 162 which are shiftably mounted in the central bores 152 of the members 146. The inner ends of the valve stems 162'terminate interiorly of the hollow valve elements 160 for abutting engagement with a plug 164 in the end of the valve element 160. A retaining ring 165 is secured to each of the valve stems 162 and engages annular shoulders 166 in the valve elements 160 to prevent the valve stems from being withdrawn from the valve elements. To ensure that the valve elements 160 will remain seated until positively unseated by shifting the valve stems 162 inwardly within the valve bores, the outer ends of the 'valve stems 162 are stepped up in diameter from the inner ends, and tapered portions 168 join the inner and outer ends and are of larger cross-sectional area than the retaining rings 164 atthe inner endsof the valve stems 162 whereby fluid pressure in the bores 152 will act to shift the valve stems outwardly and engage the retaining rings 164 against the shoulders 166 of the valve elements 160 to seat the valve elements 7 against the seats 158. The plugs 164 are spaced axially from the shoulders 166 to permit the valve stems to be shifted slightly axially inwardly without affecting the valve element for a purpose to be explained below.

Wedge-shaped cams 170 and 172 are respectively contiguous with the upper ends of and swivel with the mounting pin structures 62 and 64 during extension and retraction of the actuators 46 and 48 to automatically control, as will be more fully explained below, the positions of the valve stems 162 to reverse the flow of fluid to the actuators 46 and 48 when they reach the ends of their strokes.

The operation of the power transmission device 42 is initiated by shifting the direction control valve 110 fromits central neutral position to one or the other of the active conditions. As will become apparent from the description below, connection of the inlet 98 to the pump 104, as illustrated in FIG. 4, will result in counterclockwise rotation of the crank shaft 70 and the grader circle while connection of the inlet 98 to the reservoir 108 will result in clockwise rotation of the circle 40. Since the operation is essentially the same for either direction of rotation, only the operation for counterclockwise rotation is discussed and all directions of rotation mentioned below are with reference to the circle 40 being driven counterclockwise.

Thus, with the inlet 98 and the outlet 100 respectively connected to the pump 104 and the reservoir 108, as illustrated in FIG. 4, pressurized fluid is admitted to the upper pair of valve bores 86 and 90 between the valve stems 162 and the portions of the lower pair of valve bores 88 and 92 between the valve stems 162 are connected to exhaust to the reservoir 108. The positions of the valve stems 162, hence, the valve elements 160, determine the paths of fluid communication between the valve bores and the work ports of the actuators 46 and 48, and the positions of the actuators 46 and 48, through means of the cams 170 and 172 on the actuator mounting pin structures 62 and 64, in turn determine the positions of the valve stems 162. For example, when the actuators 46 and 48 are in the positions illustrated in FIG. 2, the piston rod 54 of the actuator 46 is halfway retracted and the cam 170 on the pin structure 62 is at an extreme counterclockwise position wherein it holds the valve stems 162 in the right ends of the pair of valve bores 86 and 88 forwardly of the line BB, shifted to retain the valve elements 160 in an unseated condition. Pressurized fluid in the valve bore 86 is thus permitted to flow around the valve element 160, into the bore 152 and out through the radial ports 154 to the control port 112 and from there to the work port 128 of the actuator 46 via the conduit means 130. Simultaneously, pressurized fluid in the actuator 46 is permitted to exhaust from the work port 132, through the conduit means 134 to the control port 116 of the valve bore 88 then into the bore 152 via the radial ports 154 and out the end of the bore 152 and around the valve element 160 to the central portion of the valve bore 88. It can be seen then that the actuator 46 is actuated to continue its retraction stroke. The actuator 48 on the other hand is 90 out of phase with respect to the actuator 46 and is fully retracted. It is at the full retracted and fully extended positions of the actuators that the cam surfaces switch from holding shifted the pair of valve stems, on one side of the line BB to holding shifted the pair of valve stems on the other side of the line BB and in this case the cam surface 172 is at an intermediate position wherein it has just released the valve stems 162 in the pair of valve bores 90 and 92 rearwardly of the line BB and has not yet shifted the valve stems 162 in the pair of valve bores 86 and 88 forwardly of the line BB. The valve elements 160 in the valve bores 90 and 92 thus remain against their seats 158 and fluid flow is blocked to and from the actuator 48. As the actuator 46 continues its retraction stroke, the actuator 48, through its connection with the crank pin 72, is rotated off-center far enough clockwise for the cam surface 172 to shift the valve stems 162 in the valve bores 86 and 88 against the plugs 164 of the valve elements 160. Flow of fluid then will occur to and from the actuator work ports 136 and 140 in substantially the same manner as described above relative to the work ports 128 and 132 of the actuator 46. The reversing valve 82 is then in the condition illustrated in FIG. 4.

When the actuator 46 is fully retracted, the cam 170 will be at its intermediate position wherein it has just released the pair of valve stems 162 in the pair of valve bores 86 and 88 forwardly of the line BB and has not yet shifted the valve stems 162 in the pair of valve bores and 92 rearwardly of the line BB. This time the actuator 48, as it further extends, rotates the actuator 46 clockwise enough for the cam surface 170 to shift the valve stems 162 in the rearward pair of valve bores 90 and 92. The work ports 128 and 132 are then connected respectively to exhaust and to fluid pressure through the bores 90 and 92.

The cam surfaces 170 and 172 act similarly to reversethe flow of fluid to the work ports of the actuators 46 and.48 when the actuators reach their fully extended positions 180 from their fully retracted positions.

To insure that the actuators 46 and 48 are overcenter before being actuated to move from their fully extended or fully retracted positions, the lost-motion connections betweenthe valve elements 160 and the valve stems 162 permit the valve stems to be shifted a limited axial distance before contacting the plug 164 to unseat the valve elements 160.

Also, it is to be noted that even though fluid pressure may exist in the bores 152, the valve elements 160 will remain seated until the valve stems 162 are positively shifted by the cams and 172 due to the cross-sectional area of the ramp 168 exposed to the pressure in the bore 152.

I claim:

1. In combination with a motor grader including a circle support frame and a circle rotatably mounted on vthe frame and including an internal annular gear; a

power transmission device for rotating the circle comprising: a source of fluid pressure; a reservoir; a pair of double-acting hydraulic actuators, each of said actuators including a cylinder and a piston rod; mounting pin structures fixedly secured to said cylinders and mounted on said circle support frame for oscillation about generally parallel axes, a crank shaft including a crank pin mounted on said circle support frame for rotation about an axis generally parallel to said lastmentioned axes, a gear integral with the crank shaft meshed with said annular gear, said piston rods being joumally connected to said crank pin, said cylinders being so positioned relative to each other and to the crank shaft that alternate extension and retraction of the piston rods will rotatably drive the crank shaft, reversing valve means connected to the source of fluid pressure, the reservoir and the work ports of the hydraulic actuator; said reversing valve means including means selectively shiftable for connecting the opposite work ports of each actuator to one or the other of the source of fluid pressure and the reservoir; and means responsive to the oscillation of the mounting pin structures for automatically selectively shifting said shiftable means for alternating the connections of the work ports of the cylinders between the source of fluid pressure and the reservoir when the piston rods are at the ends of their strokes.

2. The invention defined in claim 1 and including a pair of vertically spaced horizontal plates fixed to said circle support frame, said mounting pin structures and said crank shaft being rotatably mounted in said plates whereby said actuators are at least partially protected by said plates.

3. The invention defined in claim 1 wherein said reversing valve means includes a valve body mounted on said circle support frame between said mounting pin structures and said shiftable means including a plurality of valve stems having ends disposed adjacent said pin structures; and said means responsive to the oscillation of said mounting pin structures including cams integral with the mounting pin structures and in bearing contact with the ends of said valve stems.

4. The invention defined in claim 2 wherein said reversing valve means includes a valve body mounted on one of said plates between said mounting pin structures and said shiftable means including a plurality of valve stems having ends disposed adjacent said pin structures; and said means responsive to the oscillation of said mounting pin structures including cams integral with the mounting pin structures and in bearing contact with the ends of said valve stems.

5. A motor grader comprising: a fore-and-aft extending main frame; a triangular circle support frame having one corner universally connected at a forward location on said main frame; the support frame having opposite sides extending rearwardly from said corner; a pair of parallel spaced plates joining the sides intermediate their ends and being located one above the other when viewed in a section taken along a line bisecting the angle at the forward corner; a crankshaft journaled for rotation in said plates about an axis extending perpendicular to the plates at a location on the line bisecting the angle at the forward corner; a drive gear fixed to one end of the crankshaft for rotation therewith; a grader circle rotatably mounted on the support frame and including an annular driven gear meshed with the drive gear; said crankshaft including a crankpin; a pair of double-acting hydraulic actuators being pivotally mounted on circle support frame for movement about a respective pair of axes extending parallel to said crankshaft axis and being equispaced from the line bisecting said corner; said actuators including piston rods journally connected to said crankpin, said actuators being so positioned relative to each other and to the crankshaft that alternate extension and retraction of the piston rods will rotatably drive the crankshaft; a source of fluid pressure; a reservoir; reversing valve means connected to the source of fluid pressure, the reservoir and the work ports of the hydraulic actuators; said reversing valve means including selectively shiftable means for connecting the opposite work ports of each of the actuators to one or the other of the source of fluid pressure and the reservoir; the actuators and the crankshaft fonning a drive assembly; and valve control means extending between said assembly and the selectively shiftable means and being responsive to different drive assembly conditions during rotation of the circle for operating said selectively shiftable means for reversing flow to the opposite work ports of said actuators.

6. The invention defined in claim 5 wherein said crankpin and said actuators are located at least partially between said plates.

7. The invention defined in claim 6 wherein said actuators include cylinders having mounting pin structures fixed thereto in parallel disposition relative to said crankshaft and said pin structures being rotatably mounted in said arallel lates.

8. The inven ion de med 1n claim 7 wherein said 

1. In combination with a motor grader including a circle support frame and a circle rotatably mounted on the frame and including an internal annular gear; a power transmission device for rotating the circle comprising: a source of fluid pressure; a reservoir; a pair of double-acting hydraulic actuators, each of said actuators including a cylinder and a piston rod; mounting pin structures fixedly secured to said cylinders and mounted on said circle support frame for oscillation about generally parallel axes, a crank shaft including a crank pin mounted on said circle support frame for rotation about an axis generally parallel to said last-mentioned axes, a gear integral with the crank shaft meshed with said annular gear, said piston rods being journally connected to said crank pin, said cylinders being so positioned relative To each other and to the crank shaft that alternate extension and retraction of the piston rods will rotatably drive the crank shaft, reversing valve means connected to the source of fluid pressure, the reservoir and the work ports of the hydraulic actuator; said reversing valve means including means selectively shiftable for connecting the opposite work ports of each actuator to one or the other of the source of fluid pressure and the reservoir; and means responsive to the oscillation of the mounting pin structures for automatically selectively shifting said shiftable means for alternating the connections of the work ports of the cylinders between the source of fluid pressure and the reservoir when the piston rods are at the ends of their strokes.
 2. The invention defined in claim 1 and including a pair of vertically spaced horizontal plates fixed to said circle support frame, said mounting pin structures and said crank shaft being rotatably mounted in said plates whereby said actuators are at least partially protected by said plates.
 3. The invention defined in claim 1 wherein said reversing valve means includes a valve body mounted on said circle support frame between said mounting pin structures and said shiftable means including a plurality of valve stems having ends disposed adjacent said pin structures; and said means responsive to the oscillation of said mounting pin structures including cams integral with the mounting pin structures and in bearing contact with the ends of said valve stems.
 4. The invention defined in claim 2 wherein said reversing valve means includes a valve body mounted on one of said plates between said mounting pin structures and said shiftable means including a plurality of valve stems having ends disposed adjacent said pin structures; and said means responsive to the oscillation of said mounting pin structures including cams integral with the mounting pin structures and in bearing contact with the ends of said valve stems.
 5. A motor grader comprising: a fore-and-aft extending main frame; a triangular circle support frame having one corner universally connected at a forward location on said main frame; the support frame having opposite sides extending rearwardly from said corner; a pair of parallel spaced plates joining the sides intermediate their ends and being located one above the other when viewed in a section taken along a line bisecting the angle at the forward corner; a crankshaft journaled for rotation in said plates about an axis extending perpendicular to the plates at a location on the line bisecting the angle at the forward corner; a drive gear fixed to one end of the crankshaft for rotation therewith; a grader circle rotatably mounted on the support frame and including an annular driven gear meshed with the drive gear; said crankshaft including a crankpin; a pair of double-acting hydraulic actuators being pivotally mounted on circle support frame for movement about a respective pair of axes extending parallel to said crankshaft axis and being equispaced from the line bisecting said corner; said actuators including piston rods journally connected to said crankpin, said actuators being so positioned relative to each other and to the crankshaft that alternate extension and retraction of the piston rods will rotatably drive the crankshaft; a source of fluid pressure; a reservoir; reversing valve means connected to the source of fluid pressure, the reservoir and the work ports of the hydraulic actuators; said reversing valve means including selectively shiftable means for connecting the opposite work ports of each of the actuators to one or the other of the source of fluid pressure and the reservoir; the actuators and the crankshaft forming a drive assembly; and valve control means extending between said assembly and the selectively shiftable means and being responsive to different drive assembly conditions during rotation of the circle for operating said selectively shiftable means for reversing flow to the opposite work ports oF said actuators.
 6. The invention defined in claim 5 wherein said crankpin and said actuators are located at least partially between said plates.
 7. The invention defined in claim 6 wherein said actuators include cylinders having mounting pin structures fixed thereto in parallel disposition relative to said crankshaft and said pin structures being rotatably mounted in said parallel plates.
 8. The invention defined in claim 7 wherein said reversing valve means includes a valve body mounted on said circle support frame between said mounting pin structures and said shiftable means including a plurality of valve stems having ends disposed adjacent said pin structures; and said means responsive to the oscillation of said mounting pin structures including cams integral with the mounting pin structures and in bearing contact with the ends of said valve stems.
 9. The invention defined in claim 8 wherein said reversing valve means is symmetrically positioned relative to a line passing through the axes of rotation of said mounting pin structures. 